Remove Purple 15 color

[irfano]

Parent: https://github.com/woocommerce/woomobile-private/issues/381

Description

We don’t have Purple 15 in the Woo Color Studio. I removed it and used Purple 10 instead. Currently, Purple 15 is used as the background for tags and the warning message on the product creation screen with AI.
iOS already uses Purple 10 for the tag background, and now Android matches this design.
I didn’t add any tests since this is just a simple color change PR.

Testing information

No testing is needed. Please confirm that Purple 10 looks good on the screens I mentioned and check if I missed any screens.

The tests that have been performed

Tested tags and AI warning background.

Images/gif

before	after	iOS

• I have considered if this change warrants release notes and have added them to RELEASE-NOTES.txt if necessary. Use the "[Internal]" label for non-user-facing changes.

Reviewer (or Author, in the case of optional code reviews):

Please make sure these conditions are met before approving the PR, or request changes if the PR needs improvement:

• The PR is small and has a clear, single focus, or a valid explanation is provided in the description. If needed, please request to split it into smaller PRs.
• Ensure Adequate Unit Test Coverage: The changes are reasonably covered by unit tests or an explanation is provided in the PR description.
• Manual Testing: The author listed all the tests they ran, including smoke tests when needed (e.g., for refactorings). The reviewer confirmed that the PR works as expected on big (tablet) and small (phone) in case of UI changes, and no regressions are added.

[wpmobilebot]

📲 You can test the changes from this Pull Request in WooCommerce-Wear Android by scanning the QR code below to install the corresponding build.

	App Name	WooCommerce-Wear Android
	Platform	⌚️ Wear OS
	Flavor	Jalapeno
	Build Type	Debug
	Commit	a712c74
	Direct Download	woocommerce-wear-prototype-build-pr13137-a712c74.apk

[wpmobilebot]

📲 You can test the changes from this Pull Request in WooCommerce Android by scanning the QR code below to install the corresponding build.

	App Name	WooCommerce Android
	Platform	📱 Mobile
	Flavor	Jalapeno
	Build Type	Debug
	Commit	a712c74
	Direct Download	woocommerce-prototype-build-pr13137-a712c74.apk